The agricultural revolution was a game changer..

Why does this matter for global change?

  • Over human history…
    • Biomass of terrestrial vegetation has halved
      • 443 trees per human
    • More than 20% reduction in biodiversity
      • terrestrial and aquatic
    • At least one million species threatened with extinction
      • new discussions of an emerging mass extinction event
    • More than 70% of the Earths land surface has been altered by humans
      • only 5% is left as ‘pristine’
    • Total global biomass of wild animals today is < 25% of what it was during the Late Pleistocene
    • Terrestrial vertebrates biomass today is represented by livestock (59%) and living human beings (36%).

What else is wrong with this representation?


In addition to other harmful fallacies this cartoon propagates, it makes “being human” seem very simple, very separate, and very independent

The complexity of being human


In addition to other harmful fallacies this cartoon propagates, it makes “being human” seem very simple, very separate, and very independent

The complexity of being human


Homo sapiens wouldn’t exist without our complex evolutionary, ecological, and societal associations

Is independence just another human fallacy?


This isn’t only “external” but also internal

What does it mean to be Homo sapiens?


  • Example 1: your inner ecosystem

    • 10,000 species occupy human body

    • 80-100 genera


  • 39 trillion microbial cells including bacteria, viruses and fungi live on-in us
    • ‘cell-wise’ the human body is 43% human


  • Human microbiome has 500x more genes than human

How independent are we?


What does it mean to be Homo sapiens?



  • Example 2: (barely) hidden in your DNA


  • ~8% human genome is viral remnants


  • ~40% human genome is repetitive DNA which also likely has a viral origin


  • 100,000 pieces of ancient viral DNA live among our genes
    • function, if any, has long been unclear

What does it mean to be Homo sapiens?




  • Example 2: (barely) hidden in your DNA


  • Most humans have 2% Neanderthal DNA
    • remember - both species co-existed and sometimes mated


  • Neanderthal allele variants range in diverse expression of skin and hair color to immune function and neuropsychiatric disease
    • may have left us prone to allergies!
    • may have caused some to have higher risks from Covid!
    • possible genetic links to depression and addiction

Review: We are not ‘independent’ because we persisted

H.sapiens overlapped with 2 others for 1,000s of years

H. neanderthalensis are our closest extinct relative




  • Modern molecular tools have been able to sequence Neanderthal and Denisovan genomes


  • Denisovans left genetic traces in oceanic and Asian regions
    • genomes of Australian aborigines, New Guineans and Pacific Islanders ~6% Denisovan


  • How separate or independent our we?
    • perhaps…..just enough…..

H. neanderthalensis are our closest extinct relative




  • Modern molecular tools have been able to sequence Neanderthal and Denisovan genomes


  • Denisovans left genetic traces in oceanic and Asian regions
    • genomes of Australian aborigines, New Guineans and Pacific Islanders ~6% Denisovan


  • 87 specific genes in modern humans are different from related genes in Neanderthals and Denisovans

  • Potential clues for our survival?

Meet the Data: Has proportion of shared ancestry changed?

Fu et al. (2016) The genetic history of Ice Age Europe. Nature 534: 7606-7616

Key questions from Fu et al. 2016


Is there a particular part of the world where you would predict Neanderthal ancestry in modern human genomes would be particularly high? Why?


Do you expect the proportion of Neanderthal ancestry to increase, decrease, or stay constant over the last 50,000 years? Why?


  • Data: genomes of 51 modern humans over a time series of Europe migration
    • 45,000 - 7,000 years ago
    • taken from archaeological sites


  • Compared SNP’s = sites in genome with known variation among individuals
    • up to 1000 nucleotides of DNA is a SNP

What do the data show?

Why would ancestral Neanderthal DNA be decreasing?

Natural selection against Neanderthal DNA is likely responsible for the change, but some will likely persist

Why did humans win the survival race?

  • Was it key ‘human’ traits?
    • many of these were shared (bi-pedalism, tools)


  • Was it evolution of larger brains?
    • our we that different than Neanderthals?


  • Was it fire?
    • H.erectus may have used fire before we evolved


  • Was is related to social aspects
    • survival of the friendliest


  • Was it related to our adaptability?
    • climate was unpredictable


  • Was it something non-human?
    • superior microbiome
  • Was it luck?
    • were we ‘independent’ enough?

Next up: Friday open-discussion of human impacts

  • Humans have existed for ~300,000 years


  • For how long and in how many ways have H.sapiens altered Earth’s systems and landscapes?


  • Find as many examples as you can
    • Be creative in your search (scholarly or not)
    • think beyond Industrial Revolution and CO2


  • We will create a timeline of influence on the board
    • each of you will add something


  • We will then discuss what it all means
    • Submit your evidence (link or aritcle) on Brightspace